1. Field of the Invention
The present invention relates to a non-magnetic stainless steel and more particularly it is concerned with a low-priced and non-magnetic stainless steel for a spring, having excellent properties.
2. Description of the Prior Art
Up to the present time, SUS 304 stainless steel has widely been used as a high strength stainless steel for a spring. SUS 304 stainless steel is considered to be non-magnetic because of having an austenitic structure after a heat treatment, but SUS 304 obtained as a material for a spring is not non-magnetic because, when subjected to cold working to obtain a high strength as a spring, the austenite is partially transformed into a strain-induced martensite that is ferromagnetic. This strain-induced martensite acts also as a notch or a nucleus of fatigue fracture, resulting in deterioration of the fatigue property. In a case where a non-magnetic property is required, therefore, SUS 316 having a large nickel content has often been used. However, SUS 316 is too expensive because of containing large amounts of nickel and molybdenum and, in addition, SUS 316 is not so suitable for use as a spring steel because of containing large amounts of additional elements so that the strength is only 80 to 90% of that of SUS 304.